Test Coils Description
test coil systems have been built for investigation into the basic operational
characteristics of the coilgun. Four general purpose single stage test coils have
been constructed. These coils consist of a stainless steel tube, nylon end formers
and the coil winding. One of the formers is cross drilled to accept an optical
gate sensor. In addition to the 'drive' coils there is also a sensor coil wound
on its own former. This can be transferred between the drive coils for making
induced voltage measurements as well as testing single stage induced voltage triggering
systems. Fig 1 shows a cutaway diagram of the coil features. The tube is slotted
to reduce the eddy currents induced by the dynamic magnetic flux. Ideally a non-conducting
tube should be used but the slotted stainless steel tubing is a viable alternative.
A layer of heatshrink insulation is fitted over the tube between the formers.
This prevents a possible short circuit between the winding and the tube. The windings
are impregnated with acrylic lacquer to bind the coil together. This is useful
in distributing the electromechanical loading on the turns. There is a bit of
variation in the dimensions of the coils. I had intended them to be almost spot
on 26mm in length but it didn't turn out quite that way.
Fig 2. shows the
two stage coilgun which is intended for preliminary testing of multistage induced
voltage triggering. The coils are wound on individual nylon formers which are
permanently glued to the slotted stainless steel tube. The sensor coils are wound
directly over the drive coils and are positioned centrally along the coil axis.
The sensor coils were wound with nylon end support rings clamped onto the drive
coil allowing a compact multilayered coil to be formed. Acrylic lacquer was sprayed
into the coils and, when set, the support rings were removed. The windings were
then lightly coated in epoxy to give some additional strength.
1. Single Stage Test Coil with Optical and Induced Voltage Sensors
2. Two Stage Coilgun with Induced Voltage Sensors